Audio clip from Old Nick Theatre, Gainsborough, UK

A little audio clip taken from The Old Nick Theatre, Gainsborough, UK. A group of us were talking outside the Victorian police cells. I then heard two sounds coming from the empty male cells. Nobody was in that area and the noises remain difficult to explain. In the end, I thought the most likely cause was the empty water pipes which led to the toilets inside the cells themselves. What do you think?